The present invention relates to an optical fiber holding capillary tube that is capable of inserting and holding a plurality of optical fibers therein in an ordered arrangement, and easily positioning and securing the optical fibers in relation to other optical components.
When dividing a signal transmitted through a single optical fiber to a plurality of optical fibers, or combining signals transmitted through a plurality of optical fibers into a single optical fiber, capillary tubes have been used to hold and secure the plurality of optical fibers. When positioning and securing two optical fibers in an accurately parallel arrangement, for example, a capillary tube 1' that has an insertion hole 2' having a circular cross section is used wherein two optical fibers 5', 6' are inserted, as shown in FIG. 12.
However, since the insertion hole 2' of the capillary tube 1' has a circular cross section, in the event of the two optical fibers 5', 6' cross each other in the insertion hole 2' as shown in FIG. 12(A), optical axis 5b' of the optical fiber 5' and optical axis 6b' of the optical fiber 6' are displaced from the center axis P of the insertion hole 2' by angles .DELTA..theta.1 and .DELTA..theta.2, respectively. As a consequence, the optical fibers 5', 6' are displaced from the proper relative position with optical elements such as a light emitting element, a light receiving element, a waveguide element and optical fibers that are disposed in parallel to the center axis P, resulting in increased connection loss.
Also as shown in FIG. 12(B), a center line M' that connects the center of the optical fiber 5' and the center of the optical fiber 6' is displaced from the normal position by an angle .DELTA..theta.3 in the circumferential direction. This makes it necessary to adjust the relative positions of the optical fibers 5', 6' with other optical elements in the circumferential direction. Since some of optical fibers, so-called single-mode fibers, are as small as 5 .mu.m to 10 .mu.m in the diameter of the core where optical signals are transmitted, it may be extremely difficult to adjust the relative position described above.